1. Field of the Invention
The present invention relates to a recombinant microorganism having butanol production capacity, in which a group of genes involved in butanol biosynthesis is incorporated, and a butanol production method using the recombinant microorganism.
2. Background Art
In recent years, depletion of petroleum resources and global reduction of carbon dioxide emission have been actively discussed. It is predicted that the petroleum price will sharply increase in the future. Therefore, development of alternative petroleum materials has been awaited. For instance, there have been attempts to bioconvert biomass, sugar, starch, fat and oil, proteins, and the like, which have been produced by plants from water and carbon dioxide, into alternative petroleum materials with the use of solar energy for practical use. An example of such an attempt involves the technology of producing plant-derived polylactic acid or polybutylene succinate as an alternative plastic material made from petroleum. Further, ethanol is obtained by fermentative production from sugar, starch, or the like and blended with automobile fuel purified from petroleum so as to be used in the U.S., Brazil, and other countries.
In addition, 1-butanol is an important compound that can be used as either fuel or resin material. U.S. Pat. No. 6,358,717 discloses production of acetone, 1-butanol, and ethanol with the use of bacteria such as Clostridium acetobutylicum and Clostridium beijerinckii (ABE fermentation).
However, it is difficult to obtain high-purity 1-butanol by fermentative production. At present, 1-butanol has been generally produced by chemical synthesis from petroleum. In recent years, it has been attempted to efficiently produce 1-butanol in Escherichia coli or yeast with the use of gene recombinant technology. For 1-butanol synthesis, it is necessary to carry out the following conversion steps described below in a microorganism. Specifically, the steps are as follows: (I) a step of converting acetyl-CoA into acetoacetyl-CoA; (II) a step of converting acetoacetyl-CoA into 3-hydroxybutyl-CoA; (III) a step of converting 3-hydroxybutyl-CoA into crotonyl CoA; (IV) a step of converting crotonyl CoA into butyryl-CoA; (V) a step of converting butyryl-CoA into butyraldehyde; and (VI) a step of converting butyraldehyde into butanol.
Clostridium acetobutylicum-derived genes have been known to be involved in the above conversion steps. There are examples of producing 1-butanol by causing the expression of such genes in Escherichia coli (approximately 60 mg/L) (see Metabolic Engineering, 10. 6. 305-311 (2008) and Appl. Microbiol. Biotechnol., 77, 1305-1316, 2008). In addition, there is another example of producing 1-butanol in Escherichia coli (approximately 75 mg/L) and in Saccharomyces cerevisiae (approximately 2 mg/L) with the use of the Euglena-derived TER gene and the Clostridium beijerinckii-derived ALD gene (WO2008-137402). In addition to the above, there is an example of producing 1-butanol in Saccharomyces cerevisiae. However, the production rate was approximately 20 mg/L (WO2008-080124).
As described above, the technology for producing 1-butanol in recombinant Escherichia coli or yeast with the use of the Clostridium acetobutylicum-derived gene has been under development. However, in such case, the productivity is lower than that in the case of production of 1-butanol, at a rate of approximately 2.5 g/L with the use of Clostridium acetobutylicum (Biotechnol. Lett., 4, 29-32, 1982). Therefore, an increase in the amount of a product produced in such a recombinant has been awaited.